1. Field of this Invention
This invention relates to a process for the production of malonic acid dinitrile which involves reacting cyanogen chloride and acetonitrile in the gaseous phase at temperatures of 700.degree. to 1200.degree.C, chilling the reaction product mixture and isolating the malonic acid dinitrile from the reaction product mixture.
2. Prior Art
It is known to produce malonic acid dinitrile by reaction of cyanogen chloride and acetonitrile, both in the gaseous state, at a temperature above 600.degree.C. (see U.S. Pat. No. 2,553,406).
German Application Nos. 1,768,154 and 1,911,174, which have been laid open to public inspection, teach producing malonic acid dinitrile from acetonitrile and cyanogen chloride at a medium reaction temperature below 800.degree.C. and immediately chilling the gaseous reaction product, for example, with ice water, to a low temperature. If the reaction is carried out in the presence of water, then acid-binding substances are added.
German Pat. No. 1,281,424 teaches the reaction of acetonitrile and cyanogen chloride is described in the presence of certain catalysts at 800.degree. to 950.degree.C., or in the presence of chlorine or bromine, as a catalyst, at 700.degree. to 950.degree.C. In such process the reaction mixture is then chilled to a low temperature.
Swiss Patent No. 493,473 discloses the production of malonic acid dinitrile from acetonitrile and cyanogen chloride in the gaseous phase at a temperature of 740.degree. to 780.degree.C. At the same time a molar ratio of cyanogen chloride to acetonitrile of 1:1 to 1:5 is used. A tarry time of 1 to 15 seconds is used. The developing reaction product is cooled immediately, preferably by application of a cooling brine, to 20.degree. to 50.degree.C, and preferably to 25.degree. to 30.degree.C.
In all of the known processes, an attempt was made to chill (quench) the reaction product mixture as quickly as possible to as low a temperature as possible, because the assumption was made that the formation of secondary products could thus be avoided. As a result of such a rapid chilling to a low temperature, a part of the HCl formed during the reaction remained dissolved in the reaction mixture and resinifications developed nitrile compounds, which caused choking and incrustations both in the chilling part of the reactor as well as in the subsequent distillation. As a result of that the apparatus could only be used for a short time -- which in practice leads to the fact that these processes were hardly usable technologically. If the chilling is carried out with the help of cooled acetonitrile (see German application No. 1,768,154), then there is the additional disadvantage that large quantities of HCl are still dissolved in the excess acetonitrile and the separation of the reaction mixture is made even more difficult. As has already been explained previously, this is exceedingly difficult because of the resinification and it can be carried out only on an uneconomical basis.
If alkalis are inserted simultaneously with the chilling for the purpose of neutralizing the hydrochloric acid formed, then considerable losses of acetonitrile as a result of hydrolysis cannot be avoided and the ammonium salts formed are an additional burden to the separating processes.